The present invention relates to a brake system with an automatic braking mechanism which is used, such as, for enabling a driver of a vehicle to easily start the vehicle on a slopping road, for enable the driver to brake the vehicle for waiting a red light or in a traffic jam without continuously pedaling a brake pedal, for operating a traction control when a driving wheel slips, for holding the vehicle in a stopped state on a sloping road, for controlling the distance between the vehicle and a forward vehicle while running, for controlling the speed of the vehicle to prevent an excessive speed due to a slope, or for preventing the driver front forgetting to actuate a side brake.
As for an automobile, a brake system with an automatic braking mechanism has been recently developed. The automatic braking mechanism is used, such as, for enabling a driver of a vehicle to easily start the vehicle on a sloping road without rapidly repedaling from a brake pedal or parking brake to an accelerator, for lightening the fatigue of the driver due to the braking operation by enabling the driver to brake the vehicle for waiting a red light or in a traffic jam without continuously pedaling a brake pedal, for ensuring the stating or acceleration of the vehicle upon operating a traction control when a driving wheel slips, for automatically controlling the distance between the vehicle and a forward vehicle while running, for controlling the speed of the vehicle to prevent an excessive speed due to a slope, or for preventing the driver from forgetting to actuate a side brake.
Japanese Published Unexamined Patent Application No. H4-292256 disclosed, as shown in FIG. 5, such a brake system with an automatic braking mechanism as an conventional one.
The brake system shown in FIG. 5 is provided with a vacuum servo unit of tandem type. In this figure, the vacuum servo unit 150 is in a non-braking state in which a breather valve 151a of a valve mechanism 151 is closed and a vacuum valve 151b is opened so that chambers A, B, C, D are vacuumed. In addition, a solenoid valve 152 is normally set in a shown position so that a chamber A' surrounded by bellows 153 is normally vacuumed.
In the non-braking state, as an input shaft 154 advances upon pedaling the brake pedal (not shown) for normal braking, the breather valve 151a of the valve mechanism 151 is opened and the vacuum valve 151b is closed so that the atmosphere is introduced into the transformer chambers B and D through the transformer paths 155 and 156, respectively. Therefore, differential pressures are developed between front and rear chambers A, B and C, D of diaphragms 157, 158, the diaphragms 157, 158 and power pistons 159, 160 thus advance, an output is produced from an output shaft 161, and a master cylinder 162 operates in response to the output to actuate the normal brake.
The advances of diaphragms 157, 158 and the power pistons 159, 160 continue until the breather valve 151a is closed not to introduce the atmosphere into the transformer chambers B, D. As a result of this, the outputs become outputs magnified at a predetermined servo ratio corresponding to the input, i.e. the amount of pedaling the brake pedal. In this state, both the breather valve 151a and the vacuum valve 151b of the valve mechanism 151 are closed.
On the other hand, in the non-braking state, as the solenoid valve 152 is switched by the controller when the vehicle is in automatic braking condition that the automatic braking mechanism has to be actuated, the atmosphere is introduced into the chamber A' and further introduced into the transformer chambers B, D through a constant pressure path 163, the opened vacuum valve 151b, and the transformer paths 155 and 156, respectively. Therefore, the diaphragms 157, 158 and the power pistons 159, 160 advance to actuate the brake similarly to the aforementioned normal braking. Thus, the automatic brake is actuated upon switching the solenoid valve 152 in response to the control signal from the controller when the vehicle is in the automatic braking condition.
In this conventional brake system with the automatic braking mechanism, however, while the driver pedals the brake pedal to operate the normal braking, the vacuum valve 151b is closed to block the communication between the constant pressure path 163 and the transformer path 155. Therefore, while pedaling the brake pedal, even when the vehicle is in the automatic braking condition and the solenoid valve 152 is thus switched by the controller so that the atmosphere is introduced into the chamber A' and the constant pressure path 163, the atmosphere is not introduced into the transformer path 155. Accordingly, while pedaling the brake pedal, the automatic brake can not be actuated even when the vehicle is in the automatic braking condition.